KVM: arm64: nv: Release faulted-in VNCR page from mmu_lock critical section

The conversion to kvm_release_faultin_page() missed the requirement
for this to be called within a critical section with mmu_lock held
for write. Move this call up to satisfy this requirement.

Fixes: 069a05e5 ("KVM: arm64: nv: Handle VNCR_EL2-triggered faults")
Signed-off-by: Marc Zyngier <maz@kernel.org>